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We currently offer two different lines of HPA conversion systems. There is the Fusion Engine line which is a complete drop-in replacement for an AEG's gearbox. So, you just remove the whole gearbox and drop the Fusion Engine into the rifle in its place. Then we also have our line of cylinder conversion kits which are cylinder replacement systems for an AEG's gearbox. These reuse the original gearbox shell and simply replace the gearbox's internal components.

The PolarStar HPA conversions can be separated into two broad categories: Dual Solenoid and Single Solenoid systems. Dual solenoid systems use two solenoids to move the nozzle and fire the round. This allows each action to be controlled separately and precisely. Single solenoid systems have only one solenoid, which controls nozzle movement from it's retracted idle position to the forward firing position. The firing air is not directly controlled by the solenoid, but by the position of the nozzle as it moves forward to chamber the round.

Fusion Engine™: A complete drop-in kit which replaces the entire gearbox. It is the most adjustable system of the group with the widest range of adjustment in both velocity and rate of fire. It is a dual solenoid, closed bolt system so you are able to adjust the poppet valve (firing air) and nozzle (feeding) independently for unparalleled control over both the loading time and air volume used. Being a true closed bolt system it is easier to achieve a high level of accuracy since it is not as critical of the hop-up configuration as an open bolt system. Additionally, it does have the best feeling trigger since the trigger micro switch is custom fit to the frame so the trigger has a distinct break, hard stop and short reset.

F2™: The F2 is basically a Fusion Engine that has been miniaturized into a drop-in cylinder conversion kit like the F1 and JACK in which it replaces the components within the original gearbox shell of the AEG. Like the Fusion Engine, it is a dual solenoid, closed bolt system for complete independent control over the poppet and nozzle and delivers the performance you can only get from a closed bolt system. The F2 has a more air efficient design than the Fusion Engine and is comparable to the JACK in terms of efficiency.

F1™: An open bolt conversion kit which replaces the components within the original gearbox shell of the AEG. It is the most air efficient and uses a flow regulating check valve as well as "2-stage" firing. The unique flow control system uses an integral check valve to regulate the forward speed of the nozzle while maintaining the fastest retract speed possible. When the nozzle is traveling in the forward direction the check valve is sealed, limiting the speed of the nozzle for smoother chambering and consistent BB placement. After the nozzle travels a certain distance, it begins to allow airflow through the bore to begin the acceleration of the BB. When the nozzle reaches the forward position the check valve opens to allow the maximum flow into the barrel. The additional flow is maintained throughout the rearward travel of the nozzle, allowing it to retract without limiting its rearward speed.

In addition to the flow control and 2-stage firing, F1 also uses a custom solenoid designed specifically for this application. This allows the solenoid to become an integral part of the system rather than just a switch to control airflow. The advantages include a more compact system and a more efficient system due to the reduced internal "Dead Volume".

JACK™: Like its sister product, the F1, it is another open bolt conversion kit which replaces the components withing the original gearbox shell of the AEG. It has a simple, straight forward design which is very reliable and delivers solid performance. It has better air efficiency than a stock Fusion Engine and is only slightly less air efficient as an F1.

Kythera SA™: The Kythera is another cylinder drop-in kit which is also a closed bolt system. However, internally it is completely different from any of the above since it is a fully mechanical system and therefore does not use solenoids, a battery or any type of electronics. What sets this system apart from other mechanical systems is the design of its trigger. The trigger mechanism is designed to replicate the function, weight and feel of a real single-action firearm trigger. The sears catch and release the spool valve in the same way the sears of a real firearm catch and release the hammer or striker. This gives the Kythera trigger the distinct break and reset you would expect to feel when firing a real single action firearm.

This is a semi automatic only system but, due to its unique design, it can be fired faster than any other mechanical system.  This is because the Kythera SA completes a full shot cycle on the trigger pull without needing the trigger to be released in order for the system to complete the shot cycle. As the system resets and recharges immediately after firing, it is ready to fire again before the trigger has been released. This means that, unlike competing mechanical systems, the Kythera can cycle very quickly allowing for a high cyclic rate and lightning fast follow up shots. This gives you the proven closed bolt performance of the Fusion Engine and F2 in a completely mechanical, waterproof system with a realistic trigger.

No, our systems are designed to work with the AEG's original barrel, hop-up and magazines so nothing needs to be changed.

Three different components are needed to run our systems. You will need a regulated air rig capable of regulating output pressure to 120psi and below, a HPA (High Pressure Air) tank and a battery to power the on board FCU (Fire Control Unit).

All of our systems require minimal maintenance as each system only has at most 2 moving parts. We recommend disassembling, cleaning and greasing each system after every 30,000 to 50,000 shots.

Basically the way the system comes as stock, the poppet valve allows the maximum amount of air flow through the system and it is the nozzle which restricts the flow into the barrel which varies the velocity. This gives you a wide range of velocity adjustment by simply changing out the nozzle to shift the velocity range of your rifle up or down in large increments.

The low flow poppet valve does what the name suggests and restricts flow at the valve itself so it allows less air through. Therefore the main restriction is back further in the system instead of right up front at the nozzle. Normally, with the nozzle being the restricting point, there is air backed up in the section between the poppet and the nozzle which will only be able to vent out as fast as the nozzle's restriction allows. If a more restrictive nozzle is needed to keep the muzzle velocity within field limits, there will still be air pressurized in this section after the poppet valve has closed and the BB has left the barrel so that air is wasted. Since it is the poppet valve which turns the air flow on and off, having it being the restricting point conserves air since less air is allowed through at once.

The low flow poppet also helps improve how smoothly air flows down the barrel since it has time to expand slightly in the system after it goes through the valve so there is less turbulence behind the round which can improve accuracy slightly. With the poppet being the main restrictive point, the nozzle doesn't have as much of an affect on restricting flow although it can still restrict if the flow reaching the nozzle is still greater than the nozzle can let through at once. This is why you typically use a higher flow nozzle in conjunction with the low flow poppet such as a Black, Silver or Red nozzle. With the Red Low Flow poppet installed along with one of these higher flow nozzles, a Fusion Engine can achieve up to 50% greater air efficiency than a stock engine producing the same muzzle energy.

With the low flow poppet valve the rifle will be optimized for air efficiency when operating at standard field limits. While it may not be able to hit as high of a velocity in the maximum pressure range as it would have with the standard poppet valve, it will still be able to achieve rifleman and DMR velocities and with greater air efficiency.

Here are some examples of how a Red Low Flow affects muzzle velocity. Testing was done at 80psi and 120psi using a VFC M4 with a stock hop-up and 6.05x380mm barrel.

Red Nozzle: 400fps - 485fps w/ .20g 355fps - 415fps w/ .32g

Silver Nozzle: 390fps - 450fps w/ .20g 340fps - 390fps w/ .32g

Black Nozzle: 370fps - 430fps w/ .20g 325fps - 375fps w/ .32g

The easiest way to tell the difference between a GEN1 or GEN2 and the current GEN3 engine is by the selector plate. On a GEN3 the selector plate is black in color and is the same design as an AEG selector plate so that it slides in tracks along the top and bottom of the plate. The GEN1 and GEN2 V2 engines had a blue selector plate that is secured to the engine with a round bushing in the center of the plate.

The main difference between a GEN1 and GEN2 engine is the electronics. A GEN1 engine will have 6 wires in the harness and each wire plugs into the FCU individually while a GEN2 will have 5 and are all contained within a single white connector that plugs into the FCU.

Most likely, yes. F1 was designed to fit virtually every AEG gearbox available, including those with offset nozzles. The only things to determine are the correct nozzle and switchboard.

For most applications a JACK/F1 switchboard is already available to drop directly into the gearbox. If no switchboard is currently being made for that model, plugboards are available for custom wiring.

Single solenoid systems are required to choose between closed bolt/fixed volume or open bolt/adjustable volume operation. Dual solenoid systems like the F2 and Fusion Engine allow for the nozzle and poppet valve to be adjusted independently of each other so you are able to achieve the best possible air efficiency while getting the performance advantages of a closed bolt system.

Being able to fine tune the air volume which the system produces makes it possible to optimize air efficiency for a particular barrel length so it will only release the precise volume of air needed to fill that barrel. Fixed volume systems release a set volume of air so their air efficiency suffers in comparison.

The difference between closed bolt and open bolt is the position of the nozzle when the system it is at idle (waiting to be fired). With an open bolt system the nozzle is back and a closed bolt the nozzle is forward. When you fire an open bolt system the nozzle is driven forward so that it chambers the BB and then fires at the end of its travel before retracting back to the rear position. When you fire a closed bolt system the system will fire first, then cycles the nozzle back allowing a BB to enter the chamber before the nozzle returns forward to push it into the bucking.

A closed bolt system is more forgiving of the hop-up system since the BB is in the chamber and everything has stopped moving before the system fires. An open bolt system is more critical of the hop-up system since it is pushing the BB into the chamber and firing in the same motion so the BB never actually stops. This is why open bolt systems typically require a bit more tuning of the barrel group than closed bolt systems in order to optimize accuracy.

Dual solenoid systems allow you to change the sequence in which the system fires. Traditional "closed bolt" operation means that the system will fire air down the barrel first and then cycle the nozzle to chamber the next round. This is how all single solenoid, closed bolt systems operate. The disadvantage here is that if you run the magazine dry and load in a new magazine, the first shot will be a dry fire since the system will fire first and then cycle the nozzle to chamber the first round.

With dual solenoids you can control the nozzle and poppet valve independently so you can choose between running the F2 in traditional "Closed Bolt" mode or reverse the firing sequence for "AEG Mode". In AEG Mode the nozzle will cycle first to chamber a around and then the system fires. Therefore even if you run the magazine dry and load a new magazine on an empty chamber, the first shot will not be a dry fire.

Yes, an offset version is planned and is currently in development!

Yes, we plan to eventually have the same switchboards available for the F2 as we do for the F1 and JACK.

No, the F2 is simply another addition to our product line. The Fusion Engine will remain as our flagship product for the foreseeable future.

We will release different low and high flow poppets for the F2 however there will only be one nozzle for each model. Different levels of restriction are not necessary for the nozzles on the F2 due to the much wider operating pressure range. This allows the F2 to achieve a much wider velocity range simply be adjusting input pressure.

Yes, the F2 uses the same input fitting as the F1 so it can use the same IGL as the one the sell for the F1. The IGL is a very close fit to the lower solenoid though so it can be a bit tricky to install. They recommend keeping downward pressure on the IGL to avoid contact with the solenoid while threading it in. Or, remove the solenoids before installing the IGL and then reinstalling the solenoids afterwards.

Yes, those two holes are exhaust vents. When the system is fired, the solenoid valves open which sends air to the poppet and nozzle to drive them to their open/retracted position for the preset amount of time (dwell). When the dwell has elapsed, the air reverses back through the solenoids and vents to atmosphere through those exhaust vents.

The red poppet will be the highest flowing poppet available for the F2. After testing different poppet valves we confirmed that the standard red poppet in the F2 flows more than the air input fitting feeding the system. So, a poppet with higher flow than the red makes no difference in velocity since the restrictive point is the fitting and not the poppet.

The Fusion Engine is able to flow more through its poppet valve than the F2 since the Fusion Engine has an accumulation chamber behind the poppet valve on in additional to being fed from the input line. The F2 is only fed from the input line so it is not able to dump a large volume of air as soon as the valve opens. While this prevents the F2 from reaching the upper most velocity range of the Fusion Engine, it does make it possible for the F2 to be noticeably more air efficient at normal field velocity limits.

JACK is a centerline AEG cylinder replacement. If the gearbox uses a standard piston and cylinder assembly and the nozzle is centered in the cylinder there is a good chance JACK will fit.

In order to install JACK into an AEG, the correct nozzle is required. PolarStar manufacturers a number of different JACK nozzle lengths to cover a wide range of guns. If the nozzle length you require is not already in production, custom nozzles can be made upon request.

In addition to the nozzle, JACK must interface with the selector and trigger of the host gearbox. This is accomplished using various switchboards which install into the gearbox shell.

For more information on the compatibility of specific models please see our Compatibility Guide in the support section.

A 7.4V LiPo battery is recommended for powering the FCU. Since the battery voltage is be regulated and reduced to 5V additional voltage is unnecessary.

9V Alkaline batteries should not be used as they do not provide sufficient current to power the solenoid.

All PolarStar FCUs may be set to a semi-only mode through the selector settings.

In instances where the replica must be permanently converted, semi-only firmware is available for each PolarStar FCU model. This restricts all selector positions to a single shot per trigger pull and the ability to adjust it has been removed.

Control units may be ordered with this firmware pre-loaded. Users may send in their current FCU to be re-flashed.

Unfortunately, no. The Mini FCU was designed to work with single-solenoid systems like JACK and F1.

Although it shares the same connectors and 5-position wire harness it is only able to control one solenoid. The "unused" solenoid wire has been repurposed as an additional input in order to allow the Mini FCU to work with 4-position selectors.

To correctly set the dwell on either the F2, F1 or JACK you would first set your dP to the maximum setting of 99 and then adjust your air pressure until you are shooting at the desired velocity with the BB weight you will be using.

Then start reducing the dP by 5 at a time until you see the velocity decrease or become noticeably inconsistent. This is a sign that you are under voluming the barrel so that air flow is being shut off before the BB reaches the end of the barrel. Increase the dP by 1 at a time until the velocity and shot consistency returns to where it originally was and then set the dP 2 higher than that point.

The "iS" is the anti-stiction timer. Each number has a value of 10 seconds (i.e. 01 = 10sec, 02 = 20 sec, ect.). The timer will begin after each trigger input and once it ends it will add the value you have set in "iP" to your "dP" for the first shot.

Therefore if you have "iS03", "iP10" and "dP50", after the system has been idle for 30 seconds it will automatically increase your dP to 60 for the first shot and then lower it back to 50 for the following shots until the system has once again sat idle for 30 seconds.

Note that if you have nothing set for your iP (i.e. iP00) then it will not add an extra plus to the dP regardless of what you have iS set to. The iS is simply a timer.

To program a fire mode to each selector position you would adjust the S1 and S2 settings in your FCU programing menu. On most common rifles such as an M4, the S1 is your semi auto selector position and S2 is your full auto selector position. By default the S1 should be set to S101 for Semi Auto, and the S2 should be set to S200 for full auto. Changing the number will change the fire mode set to that selector position.

00 = Full Auto, 01 = Semi Auto, 02 = 2 Round Burst, 03 = 3 Round Burst, etc. on up to 09 = 9 Round Burst.

The semi auto delay mode is available on FCU's that have firmware revision rE1.0 and higher. To program it, enter programing mode and scroll to the "Sr" menu. The default is Sr0F (off). If you press up on the joystick you will change it to Sr01 which is a 0.1 second delay in-between shots. You can continue to increase that number in 0.1 second increments up to Sr99 which is a 9.9 second delay in-between shots.

To view the shot counter you simply enter programing mode so that you can see the revision number (e.g. rE1.2) and then hold the joystick in the down direction. It will display a 4 digit alphanumeric number. Type that into an online hexadecimal converter and it will give you the number of shots that FCU has cycled. If you have a "high mileage" engine and you have reached the maximum number for those 4 segments, the count will continue to another 4 segments which can be viewed by pressing up on the joystick. Those are simply placed in front of those displayed on the "lower" display.

For example, the down direction on the joystick displays 3bcE and the up direction displays 0006. You put the 6 in front of the 3bcE so you have 63bcE which equals 408,526.

To reset a Classic FCU, you would hold in on the joystick while you plug the battery in. The screen will display DEFT until the joystick is released and all settings will revert back to factory default.

To reset a Mini FCU, hold back on the trigger while plugging in the battery and keep the trigger held for longer than 5 seconds before releasing. The settings will reset to factory defaults and it will enter the programing main menu upon releasing the trigger.

The main setting that affects trigger response is your cb setting which simply changes the firing sequence. The default setting is cbof which means when the trigger is pulled the nozzle cycles first to chamber a round and then the poppet will fire. With cbon the poppet will fire first and then the nozzle cycles to chamber the next round.

With cbon it replicates the action of a closed bolt firearm whereas with cbof it replicates the action of an AEG. The benefit of having closed bolt on is that you will get a faster trigger response and, when shooting semi auto, it guarantees the nozzle is forward and sealed before the shot is fired regardless of other settings. This promotes improved accuracy so it is an ideal choice for Sniper/DMR applications. The only downside is that if the chamber is empty, such as when you run the magazine dry, the first shot after loading a new magazine will be a dry fire since it must fire first before the nozzle will cycle to chamber the next round.

We only recommend running our systems on HPA or Nitrogen. While liquid propellants such as CO2 technically can be used, it is required that the air delivery system be specifically designed to use CO2 and properly utilizes an expansion chamber to safeguard the system from pressure spikes.

The SLP rigs require that you use an HPA tank that has a SLP (Super Low Pressure) regulator. All tanks have an integral regulator that takes the tank's raw pressure (e.g. 3,000psi.) and reduces it to the output pressure of the tank itself (i.e. the pressure that comes out of the tank and goes into the air rig). This pressure is then reduced further by the regulator on the air rig which the tank attaches to. The SLP tanks produces 300psi or less while "traditional" HPA tanks produce over 800psi. Therefore you can only use a SLP air rig with a SLP tank so as to not over-pressurize and break the air rig while an air rig like our MRS or Micro Reg can use either SLP or traditional HPA tanks.

There are two basic types of HPA tanks on the market. The 3,000psi tanks are typically made from aluminum and are the least expensive of the two. However, the higher pressure 4,500psi tanks are carbon fiber so they are lighter and will last for more shots per fill than a 3,000psi tank of the same size.

The standard MRS is adjustable from 40psi up to 145psi depending on the input pressure of the tank. However, an optional High Pressure Spring is available which boots maximum pressure to ~200psi.




While an F2 offset system can technically be installed into a Tokyo Marui or CYMA M14 without modification, there are minor modifications that can be done to ensure the best fitment and easier air routing. These modifications can be accomplished using a Dremel tool or file.

The first modification is done to the left gearbox shell where the sector gear meets the piston track. Removing material from the upper right section of the lip surrounding the sector gear as shown will provide adequate room for the F2’s flag allowing the gearbox shell to close fully without any gaps between the two halves.

CYMA M14 Gearbox Mod1

The second modification is to the right gearbox shell in the reinforced area around the bevel gear. Removing material as shown will provide an unobstructed passage for the airline allowing it to pass through the gearbox without needing to be bent around the reinforced area.

CYMA M14 Gearbox Mod2

Once these modifications are completed the cylinder can easily be placed into the gearbox shell and you can close the gearbox shell. Before doing so you will need to solder the included trigger leads to the contacts on the original trigger switch as shown and connected to the plugboard.

The plugboard will have four 2-pin headers and one 5-pin header. The 5-pin is for the main wiring harness. The 2-pin headers are labeled CON1 through CON4.

CON1 = Nozzle Solenoid, CON2 = Poppet Solenoid, CON3 = Selector Input, CON4 = Trigger Input.

Since the M14 kit is semi-auto only, CON3 will remain empty since there is no selector support.

Route the trigger leads, wire harness and airline through the rear of the gearbox as shown. Ensure that the solenoid power leads are tucked up out of the way so as not to get pinched when the gearbox is closed up.

CYMA M14 Gearbox Mod3

The wire harness and airline will get routed out through the underside of the motor cage and to their respective locations in the stock and grip. A small hole will need to be drilled in the grip for the airline to exit through.

CYMA M14 Gearbox Mod4


Before being able to address the issue you will first need to determine if the issue is related to the system's electronics or if the selector pate or cut offer lever of the engine/gearbox is simply not interacting with the micro switch correctly. However, before diving into the inner workings of the system, you will want to check that the selector positions are in fact programed correctly in the FCU.

For the Classic FCU with the LCD screen running firmware rE1.0 or higher, you would go about programing a fire mode to each selector position by adjusting the S1 and S2 settings in your FCU programing menu. On most common rifles such as an M4, the S1 is your semi auto selector position and S2 is your full auto selector position. By default the S1 should be set to S101 for Semi Auto, and the S2 should be set to S200 for full auto. Changing the number will change the fire mode set to that selector position.

00 = Full Auto, 01 = Semi Auto, 02 = 2 Round Burst, 03 = 3 Round Burst, etc. on up to 09 = 9 Round Burst.

If both S1 and S2 are set the same then the rifle would operate the same regardless of the selector position. (e.g. having S101 and S201 would cause the rifle to only shoot semi auto)

If the selector switches are programed correctly you would then go on to check that the electronics are working correctly. To check this you'll first need to remove the engine or gearbox from the rifle so you can see the micro switch. If it is a Fusion Engine, or a V2 cylinder replacement kit such as the JACK, then you would be able to see the micro switch from outside of the gearbox. If it is a V3 cylinder replacement kit then you would need to open the gearbox to clearly see the micro switch.

With a Fusion Engine or a Version 2 cylinder kit the micro switch is located on the back side of the switchboard and is activated by the selector plate as it passes over top of it. The switch will be a little square block with a black fin sticking up. The black fin is depressed by the plate as it passes over top of the switch.

With a Version 3 cylinder kit the cut off lever depresses a micro switch at the bottom of the levers arc of travel as the lever is moved by the selector plate.

To check if the electronics are working you would simply depress the micro switch manually with you finger. If you have a Classic FCU with the LCD screen then you can verify if the FCU is receiving a signal by observing if the LCD display changes between fire modes (e.g. "Shot" and "Auto") when the switch is depressed. If it does then you will know the electronics are working correctly and the issue is simply that the switch is not getting depressed when the selector plate or cut off lever moves. For that you would need to observe how the plate or lever moves and make adjustments accordingly so that it depresses the switch.

If the system does not change fire modes with the button is manually depressed then the issue could be with the switchboard, wire harness or the FCU itself. If the issue is with the trigger board or wire harness, then it should be visually obvious that there is damage with either the switch being broken off or a wire being cut or broken.

A faint buzzing/crackling sound is fairly common since the solenoids do not have a bubble tight seal and often make that noise when under pressure as some air is able to seep through. Solenoids this small do not have a very tight seal in order to reduce fiction and maintain a fast response time with the limited capacity of the small coils. Although some air is allowed to seep through, it is such a minute amount that it will not have any detectable affect on air usage and will not even register on a flow meter.

However, you should only be able to faintly hear it in a quiet area with little to no ambient noise and is not loud enough that you would be able to hear it while outside using the rifle. If it is loud enough to hear while out in the field then it is something that should be addressed.

It is a common misconception that converting a rifle to HPA will automatically make it shoot farther and more accurately. Now, while an HPA system does have the capability to produce very consistent muzzle velocity which in turn promotes better accuracy, in the end range and accuracy comes down to the capabilities of the rifle's barrel group and the BB you are shooting through it and not the system that simply propels it. There unfortunately isn't a clear cut answer to what will produce the best performance for you as there are many different variables which could affect the accuracy and range of an airsoft rifle.

However, a good starting point is to understand the basic principles behind airsoft ballistics. The range and accuracy of your rifle is affected by a combination of four main factors.

(1) The stability/consistency of the BB's backspin.
(2) The quality/cleanliness of the inner barrel.
(3) The velocity of the BB.
(4) The weight and quality of the BB.

The stability/consistency of the backspin is a big part of how far that BB will fly. Think of spinning a quarter on a table. If you get a really good spin that quarter will stay up on its edge for a really long time despite gravity pushing down on it. If the quarter is spun off balance and is wobbling, well it won't stay up very long. The same physics apply to a BB. If it has a stable backspin in flight and the hop-up can produce that same spin shot after shot, the BB will carry further with more consistent accuracy regardless of how fast it going. So, investing in a good chamber/bucking/nub combination and having it properly installed is a good place to start.

We have found that Flat Hop buckings are one of the better ways to go since they have a wider contact patch which imparts the backspin on the BB more gradually than a traditional hop-up buckings. Since the initial acceleration of the BB is much faster with an HPA rifle verses an AEG, the BB responds to how the backspin is applied differently. Therefore you may find that you'll need to change your hop-up configuration after converting the rifle to HPA to achieve proper accuracy even if it shot well as an AEG.

Now theoretically, the longer the barrel, the longer the BB has to stabilize which could improved performance. However, getting a really good backspin out of the chamber is far more important and will have a much larger affect on range and accuracy than simply using a longer barrel.

As far as the barrel itself, we honestly have only had experience with a small percentage of the many brands out there. Overall there typically doesn't seem to be a night and day difference between brands. The one thing we did note is that brass and steel barrel typically do perform better than aluminum though. As far as tightbore vs. widebore, you can get better air efficiency from a tightbore but you do see a slightly more consistent shot grouping from a wide bore at longer ranges since the promote a more stable backspin.

A quality barrel is obviously also important but you also need to make sure it is clean. A lot of the brands of biodegradable BB's out there today will actually leave a residue behind after a while which will really screw with the stability of the BB. Think back to when you were a kid and you used to go sliding head first down a sliding board. If the board was clean and smooth you shot down as straight as an arrow going mach 2 with your hair on fire. If the board had rough patches or was wavy you would bounce around, get pulled into the sides and have a slower, less comfy ride. The same thing applies to your barrel. If the bore is clean, smooth and free of residue then the BB will just glide right on through. However, if you get a build up of residue it creates patches of friction which can cause the BB to spin off balance and ruin your accuracy and the effectiveness of your hop-up.

Velocity can make a difference in range since even if the BB doesn't have good backspin, a high velocity rifle can still hurtle the BB out to a good distance. Add that to a good backspin and you have a winning combination. However, velocity is not as important when it comes to range as you might think. Even a difference of 50 fps at the muzzle may only mean the round will go another 10 or so feet further as long as you have a good backspin on the BB. You also don't want to be shooting at an excessively high velocity or the BB will be buffeted too much which can lead to erratic trajectory. Generally you'll find that you want to stay below 350 fps with whatever you are shooting to avoid this.

The weight of the BB also plays a big role since a heavier BB will hold its energy longer than a lighter round and that energy will carry it farther. A heavier round is also less susceptible to wind and air currents which promotes better shot consistency. When shooting outdoors we never recommend shooting anything lighter than a .28g for this reason.

And lastly, the quality of the round fired, as with any shooting situation, is an important thing as well. A well balanced, highly polished round that is produced with consistent weight and uniform size will always yield better performance than one which is not. We mainly stick with High Power Airsoft (HPA) brand BB's since they are very high quality and offer a wide range of BB weights.

With any kind of gun that uses compressed gas (HPA, Green Gas, CO2), the length of the barrel greatly affects the velocity the system can produce. The affect is much greater than with an AEG since AEG's operate with very limited air volume and the initial acceleration of the BB is slower.

We use a standard VFC M4 to benchmark the specifications for our systems and that rifle uses a 6.05x380mm barrel. As an example, with that barrel the F2 produces ~250fps - 480fps w/ .2g within the 45-145psi operating pressure range. If you go down in barrel length the velocity adjustment range will shift down so your maximum potential velocity will decrease. If you use a longer barrel, everything shifts up.

If you have a 250mm barrel then you will not be able to reach 480fps with a .2g. With that same F2 in a TM MP5 which has a 229mm barrel, the maximum velocity was reduced to 375fps w/ .2g @ 145psi. One thing to keep in mind though is that, unlike with an AEG, the muzzle energy changes significantly when you change BB weight. This is due to the amount of air volume the systems produce so they can accelerate a heavier BB at nearly the same rate as a lighter one.

For example, if that MP5 was an AEG and it was shooting a .2g at that 375fps and you chronoed it with a .28g, your muzzle velocity would drop to about 317fps. With an HPA it only drops to 345fps. That means you gained about 0.25J of muzzle energy which is the difference between 375fps and 410fps w/ .2g.

If upon firing a single shot you see two BB's exit the barrel it means that the bucking lips are not providing enough resistance against the BB. The bucking lips should keep the BB from entering the chamber until the nozzle comes forward to push the BB into the chamber. If the lips do not provide enough resistance, the force of the magazine spring pushing up on the BB's can overpower the bucking lips and force the BB into the chamber so that a second BB feeds up behind it. Therefore when the nozzle comes forward it pushes the second BB into the chamber as well so both fire in the same shot.

This could be caused by either the bucking being oily so there is reduced friction and easier for the BB to slip through. The bucking lips could also be too thin or the bucking does not fit in the chamber correctly so the lips are being spread apart. Lastly the bucking could be ripped so the lips could easily separate and not provide any resistance. You should start by removing the bucking and inspecting it for damage. If no damage is found, try washing the bucking with dish soap and water to remove any oil from it. If this does not correct the issue you should replace the bucking.

Our cylinder conversion kits such as the F2 use the AEG's original mechanical safety to block the trigger from depressing the trigger microswitch just as it would have as an AEG. There isn't an electronic safety on the switchboard so the mechanical safety lever must be retained to have a functional safety.

If the safety is still in place, just double check that it was installed correctly so that it can pivot up and block the trigger. Also, if you happened to install an adjustable trigger and have it adjusted for a very short pull, the trigger could be adjusted so far that the safety lever will not have enough clearance to pass in front of the trigger.

If the system appears to be functioning correctly but refuses to feed then the issue could be caused by the solenoids being plugged into the wrong headers on the switchboard. If the solenoid controlling the nozzle is plugged into the poppet solenoid header and the solenoid controlling the poppet is plugged into the nozzle solenoid header then the nozzle will still retract and the poppet will still fire but the rifle will not feed.

This is because the solenoid is now running on the wrong dwell setting. The dwell for the poppet is much shorter than the dwell for the nozzle so the solenoid is not being energized long enough for the nozzle to retract the proper distance or length of time for a BB to feed up into the chamber. If you've recently had your system apart for upgrade/maintenance and it refuses to feed now that it is back together, checking where the solenoids are plugged in is a good place to start.

To easily determine if the solenoids are plugged into the wrong headers you will simply need to go into your settings and turn the nozzle dwell all of the way down to dn00 (or dn01 depending on the firmware). With the nozzle dwell turned all of the way down the nozzle should not retract when the system is fired but air should still come out of the nozzle. If you find that the nozzle still retracts but very little or no air comes out, then your solenoids are plugged into the incorrect ports and need to be swapped.

The Fusion Engine and F2 come from the factory with the poppet solenoid marked with a black mark on the bottom of the solenoid connector. Unless the solenoids or the solenoid power leads were psychically swapped then the solenoid with the black mark will plug into the header marked J2. If the solenoids were replaced at some point and are no loner marked, you can identify them by their position.

For the Fusion Engine, the solenoid which controls the poppet will be positioned in the manifold in-line with the shortest of the two clear air lines (left side of engine).

For the F2, the solenoid which controls the poppet will be positioned to the lower left of the cylinder as you are looking at the back of the cylinder.

Different manufactures can hold different tolerances in their models so sometimes the alignment of the selector switch assembly is slightly different from others. If this happens you may not be able to switch between the fire modes correctly or possibly not go into full auto or go into safe. Most commonly the mechanical safety will not fully disengage the trigger when moving the selector from safe to semi so that the trigger "snags" on the first pull or acts like the safety is still engaged. You can first try replacing the selector plate on the Fusion Engine with the original selector plate from the AEG. If this does not correct the issue, the Fusion Engine selector plate can be modified.

These issues are caused by the contact plate area on the selector plate being narrower than on the TM spec selector plate which is provided with our engine. Therefore it would not interface with the safety block correctly until the selector plate was modified so that the safety block will complete disengage when switching between safe and semi. Therefore some material needs to be removed from either the leading edge of the selector plate where it touches the safety lever (the P shaped part) or material can be removed from the safety lever. It is best to remove a little material at a time using a grinding wheel or file following the profile as shown and reinstalling the engine to test. You may have to do this a couple of times until enough material has been removed to allow proper function of the selector switch.

Feeding issues could be caused by a number of things unfortunately so you have to go through a process of elimination to determine the source of the problem. You'd want to start out with the normal airsoft stuff such as trying different BB's, magazines and possibly hop-up components in case any two don't want to work together.

The settings of the FCU can also affect feeding. Typically the factory default settings on the FCU will work with practically any rifle but sometimes you do need to adjust them for best performance. The setting which directly affects the feeding of the BBs is the "dn" setting which is your nozzle dwell. This is how long the nozzle is held back out of the chamber. The number represents time in milliseconds so if BB's are not feeding or are skipping shots then you will want to increase that number to allow more time for the BB's to feed up into the chamber before the nozzle starts to return forward.

The default dn is 14. To experiment, try increasing the dn by 5 at a time and see if the rifle starts to feed correctly. If it does, start backing the number down 1 at a time until it starts to act up again. Then increase it back 2 and that should be the lowest you can go on the dn with that particular combination of nozzle, pressure, magazine and BB weight.

It is likely that there may be some foreign debris on one of the poppet valve o-rings which is allowing air to bypass it. The F2 is pretty simple inside so it isn't very difficult to disassemble and reassemble. If you have never maintained your F2 before, please refer to our F2 Maintenance Video.

Once disassembled, take the poppet valve and inspect the o-rings on the poppet valve. It is the larger of the two o-rings that would allow air to leak through the center of the nozzle when you air the system up. Something would need to be on that o-ring in order for air to bypass this o-ring so be sure to clean it off and apply a very small amount of TechT Gun Sav grease before reassembling.

While the rF setting on firmware rE1.0 and higher will adjust the cyclic rate (rate of fire) of the system in actual rounds per second, with a dual solenoid system the rate of fire will be limited by where the other delays and dwells are adjusted to. Therefore, if the rF is set to 18, the engine will produce 18 shots per second but only if the other delays and dwells could be accomplished in that amount of time.

For example, if you were to set the rF to 30 rounds a second yet the dn, dr and dp were set high enough that only 23 rounds a second were possible, the engine will only produce 23 rounds a second until the dwell/delay on those other settings were reduced. Therefore by optimizing those settings you will be able to achieve the highest rate of fire possible with this particular set of variables. By following the "fine tuning" section in the FCU Manual, you will be able to optimize your FCU settings to best match the potential feed rate of your airsoft replica and therefore achieve the highest rate of fire possible with its current configuration. 

The aftermarket IGL lines that other manufacturers make for our Fusion Engine does not seal at the same point as the original PolarStar fitting. Our fitting will seal to the surface of the cylinder using a crush washer which is that little white disc. The fitting on the IGL doesn't have a shoulder so it can't use a crush washer to seal in the same way. Because of this they send the IGL with black teflon tape around the treads to create a seal there instead.

The black teflon tape is not the best at creating a seal though and if you ever take the IGL out it will require that new teflon tape be applied. What we recommend is removing all traces of the teflon tape from the IGL fitting and the tapped hole in the Fusion Engine cylinder and then applying high pressure thread sealant to the threads of the IGL.

We recommend Loctite 545 thread sealant for this application. Just a drop or two of this placed about two threads back from the end of the fitting will be all that is needed to create a seal. Just apply the sealant, snug the fitting down (30 ft/lbs recommended) and allow a few hours for the sealant to cure before pressurizing the system. 

First make sure the FCU is in the correct mode. If the FCU is in single solenoid mode then only the solenoid controlling the poppet would be actuated.

What you will need to do is press in on the FCU joystick to enter programming mode and then cycle through the menu until you come to the FCU mode which starts with FC. If the mode is set to FCF1 then you will need to click the joystick once in the up direction and it will change to FCFE.

If the FCU is in the correct mode, the next most likely cause would be the wire harness or solenoid power leads. For that, open the gearbox and check the black wires coming from the back of the solenoids to the switchboard. It is possible for these wire to get in the way when closing the gearbox and get pinched between the two halves. If you see a section of the wire which is flat, that is due to it getting pinched and the wire inside is damaged so it would need to be replaced with a new power lead.

If the solenoid power leads look fine, next  hold up both ends of the main harness next to each other with the ends oriented in the same direction. Check if the sequence of colored wires is the same on both ends. Also, check if any of the wires look to be damaged such as being broken, frayed or is pulling out so that a lot of the metal pin is showing. If any of these things are found, it would need to be replaced with a new wire harness.

This issue is consistent with having the FCU set to dual solenoid Fusion Engine mode instead of the single solenoid F1/JACK mode. In Fusion Engine mode the default dwell (dP) is much lower as well as there being unneeded operations running for the second solenoid that your system does not have.

If the dwell is too low then the solenoid will not be pulsed long enough to drive the nozzle all of the way forward to the firing position so it will only make the nozzle flinch. What you will need to do is press in on the FCU joystick to enter programming mode and then cycle through the menu until you come to the FCU mode which starts with FC. If the mode is set to FCFE then you will need to click the joystick once in the down direction and it will change to FCF1. The default dwell in this mode is dP50.

This dwell should provide reliable operation for the system down to around 60-70psi and then you might need to increase the dwell slightly. At lower pressure the nozzle will travel forward slower so more dwell (time) is needed for the nozzle to reach the fire position.

When the issue is either that the nozzle locks forward and continues to vent air out through the nozzle after the trigger is pulled, or if air leaks out of the nozzle as soon as the air line is connected, then the issue must be related to air bypassing one or more of the o-rings on the nozzle.

There is a chance that something came in through the air line and has gotten stuck to the o-ring which is compromising the seal. Typically such an issue can easily be corrected if it is simply debris that has gotten into the system. If you are comfortable opening the system then it can usually be corrected in a matter of minutes. What we would recommend doing is unscrewing the front cylinder and removing the nozzle. Then actually removing all of the o-rings from the nozzle. They can be removed with an o-ring pick tool or something similar like a toothpick. Often times the debris can get trapped under the o-ring which is why we recommend taking them off and not just cleaning the outside of the nozzle.

Once removed, wash the o-rings off with dish soap and water to remove any small bits of debris which might be hard to see. Also, wipe clean the grooves of the nozzle itself with a clean cloth to remove any debris from them as well. Sometimes it only takes a very small piece of debris in just the right place to cause an issue so it might not be something that is readily apparent when you inspect the nozzle so we recommend cleaning everything. Once everything is clean and dry, reinstall and lubricate the o-rings with more grease before reassembling. We recommend TechT Gun Sav grease for a lubricate. Traditional AEG gear grease or any type of oil should not be used.

When you reassemble the system we suggest inserting the nozzle into the front cylinder first, then inserting the donut (larger round silver piece with the radial holes) with its thin o-ring into the back of the nozzle. For the JACK, also press the stem into the back of the donut at this time. Then screw that whole assembly onto the rear cylinder. This will keep everything in place as you screw the two halves together.

If you are having reset issues then there are a few things we can have you check.

1. Do you have any of the adjustment screws installed for the main sear or disconnector? If so, it is possible that they are not adjusted properly. An easy way to determine if these are the cause is to simply remove them completely and see if the engine works correctly. Note that we do ship the Kythera with the adjustment screw for the main sear (#10) installed to keep the trigger link locked in place during shipment. This does need to be removed completely before you attempt using the system.

2. Do you still have the reset cable assembly installed? The reset latch interlocks with the spool valve to keep it from rotating. So, if it were removed and the spool valve is able to rotate a little, it will change how the disconnector interfaces with the sear on the spool valve which can result in it not wanting to release.

3. Make sure you are operating within the proper pressure range for the spring installed. The standard "light" spring is best for 60-130psi while the additional "heavy" spring is only intended for use above 90psi. If the heavy spring is used below 90psi then the system will not always recock correctly.

4. Check that the spring on the trigger link is not damaged. We had received some reports of the springs getting damaged in shipping due to the box being dropped and the system shifting forward against the insert. The coils of the spring should be stacked vertically. If the spring looks like it is bent so that the coils are offset to one side, that will change the force of the spring which would make it more difficult for the trigger to reset.

5. If you check under the spring you will find a shim stack in the pocket of the trigger link. These are there to pre-load the spring. There should be 4 shims. With 4 shims the trigger should be able to reset correctly without the trigger weight screw being installed and/or adjusted. However, additionally washers can be added to increased the spring's pre-load if needed.

6. Try testing the system with it outside of the gearbox shell. If it works outside of the shell but starts to have reset issues once it is reinstalled in the shell, check the sides of the trigger link for any rub marks. Some gearboxes might have slightly different features/tolerances that will not provide the link quite enough clearance. If the link is rubbing it will put more drag on the link and make it more difficult for the spring to reset the link. If you find this to be the case, either the sides of the link or the thing in the gearbox it is rubbing against can be sanded down for properly clearance.

If you are seeing that the rifle is skipping shots or is refusing to feed at all, it is typically a result of the nozzle cycling faster than the magazine can feed a BB up into the chamber while the nozzle is retracted. The simplest way to combat this is to install a more restrictive metering screw. While with the electro pneumatic systems you can adjust the timing in the FCU, with the Kythera being fully mechanical you have to change the metering screw in the rear cylinder to adjust nozzle "dwell".

Typically the 0.029" screw which it comes standard with works fine but in certain cases you might have to step down to the 0.024" or 0.019". If it is skipping shots more than feeding them, you might need to go down to the 0.019". One way to experiment is to lower the operating pressure to the lowest (60-70psi) which will slow the nozzle speed slightly. If you find that the rifle feeds normally, or at least greatly improves, the 0.024" should be okay. But, if it just improves slightly, the 0.019" is most likely needed. 

However, since the included 0.029" does provide enough dwell to allow proper feeding at the average magazine feed rate, you can also look into why the gun isn't able to feed BB's fast enough to keep up with the system. This can be from such things as a weak magazine spring, lower grade BB's, a bucking that isn't seated properly in the chamber or poor interface between the chamber and the magazine.

There have been several reported issues when using the Maxx triggers with our systems. It seems that their triggers are not manufactured to the same spec as other triggers and do not sit as close to the left side of the gearbox as they should. They have caused issues with all of our systems but mainly with the Kythera. With the Kythera it seems to cause the trigger to slip off the trigger link which causes the system to malfunction and eventually causes damage to the leading edges of the two components.

If you are experiencing this issue then we recommend discontinuing use of the Maxx trigger and select an alternative trigger model.